Thermostat with double pole switch

ABSTRACT

A double pole thermostat is disclosed in which two switches are mounted in separate switch cavities separated by insulating material so that arc splatter cannot produce a conductive path between the switches. The switches are sequentially operated by a bimetallic snap disc with a first bumper extending between one switch and the disc, and a second bumper extending between the two switches. The second bumper provides lost motion to insure sequential operation of the switches and to insure that unequal contact wear will not result in one switch blocking the other switch open.

United States Patent Snider et al.

[ 51 May 9,1972

[54] THERMOSTAT WITH DOUBLE POLE SWITCH [72] Inventors: Harold F. Snider; Anton J. Gerich, both of Mansfield, Ohio Therm-O-Disc, Incorporated, Mansfield, Ohio [22] Filed: Jan. 19,1970

21 Appl.No.: 3,729

[73] Assignee:

[52] US. Cl ..337/367 [51] Int. Cl. ..H0lh 37/70 [58] Field of Search ..337/41,44, 340, 354,87,63,

[56] References Cited UNITED STATES PATENTS 3,236,997 2/1966 Huffman ..337/337 3,207,876 9/1965 Mertler ..337/340 3,405,380 10/1968 Ribbs 3,500,278 3/1970 Them ..337/354 Primary E.\'aminer--Volodymyr Y. Mayewsky Assistant E.\'aminerF. E. Bell Attornqv-McNenny, Farrington, Pearne & Gordon [5 7 ABSTRACT A double pole thermostat is disclosed in which two switches are mounted in separate switch cavities separated by insulating material so that are splatter cannot produce a conductive path between the switches. The switches are sequentially operated by a bimetallic snap disc with a first bumper extending between one switch and the disc, and a second bumper extending between the two switches. The second bumper provides lost motion to insure sequential operation of the switches and to insure that unequal contact wear will not result in one switch blocking the other switch open.

4 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION This invention relates generally to thermostatically operated switching devices and more particularly to a novel and improved thermostat having a plurality of switches operated by a single snap element.

PRIOR ART Thermostatic switching devices having a plurality of switches operated by a single snap disc such as a bimetallic snap disc are known. Such thermostats are usually referred to as double pole thermostats since they provide two separate switches. Examples of such double pole thermostats are illustrated in the U.S. Pat. Nos. 2,538,080; 2,645,692; 3,272,946; and 3,435,189. These prior art double pole thermostats are provided with a structure in which both switches are located in a single cavity and are operated by a single bumper element or the like. In such devices failure can occur as a result of arcing between the two switches or between one switch and a conductive member having an electrical potential different than the potential of the switch. One cause for such failure is a buildup of arc splatter which can produce a conductive path between such elements of different potential. The practice in the past has been to provide large spacing between elements of different potential to reduce the tendency of arcing failure.

SUMMARY OF THE INVENTION The present invention has several important aspects. In accordance with one aspect of this invention a simple, low cost double pole thermostat is provided which includes a body assembly providing a separate switch cavity for each of the switch assemblies. The separation is arranged so that the tendency for arcing between the switches or between either switch and conductive elements of different potential is substantially reduced. Because the switches are located in separated switch cavities, a buildup of switch splatter does not result in any tendency to provide a conductive path between the switches.

In accordance with another aspect of this invention the switches are sequentially operated by bumper means arranged so that unequal wear of the switch contacts does not result in a malfunction of the device. The illustrated embodiment of this invention includes a body assembly providing two separate switch cavities completely separated by electrically insulating material. Two similar switches are mounted on the body assembly with one switch located in each switch cavity. A bimetallic snap disc is mounted on the body to operate the two switches in response to thermal changes.

A first bumper member extends between the snap disc and the mobile contact of the first switch and is proportioned to operate such switch in response to movement of the snap disc between its positions of stability only after such disc is in snap motion. A second bumper extends between the mobile contact of the first switch and the mobile contact of the second switch and operates a second switch in response to movement of the mobile contact of the first switch after the snap disc is in snap motion.

The second bumper is sized so that the first and second switches are operated sequentially and so that the first switch cannot block the second switch in the open position, even if a certain amount of uneven wear occurs in the contacts of the two switches.

In the particular embodiment illustrated, the two bumpers are sized so that each bumper provides an amount of lost motion substantially equal to one-third of the disc movement within its snap range, and the switch operated by the first bumper is open prior to the switch operated by the second bumper. With this arrangement the tendency for stalling of the disc is reduced when compared to such a device in which both switches operate simultaneously. Further, if the contacts of the second switch wear at a rate faster than the contacts of the first switch, the first switch does not block the second switch in the open position unless the difference in wear is excessive.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation in section of a thermostat incorporating this invention illustrating the positions of the elements when both of the switches are closed and the disc is in a position at one extreme of its snap range;

FIG. 2 is a schematic illustration of the mechanism of the thermostat of FIG. 1 illustrating the position of the elements when the disc has traveled through a distance equal to about one-third of its snap range and immediately before the first switch opens;

FIG. 3 is a schematic view similar to FIG. 2 illustrating the mechanism when the disc has moved through about two-thirds of the snap range travel when the first switch is open and the second switch is about to open; and

FIG. 4 is a schematic illustration similar to FIGS. 2 and 3 illustrating the mechanism when the disc has reached the position at the other extreme of its snap range and both of the switches are open.

Referring to FIG. 1 the illustrated thermostat incorporating this invention includes a body assembly 10 consisting of a lower body member 11, an intermediate body member 12, a cap member 13, and a disc retaining cap 14. Preferably, the body members ll, 12, and 13 are formed of insulating material such as a phenolic resin. The various members of the body assembly may be held together by any suitable fastening means such as rivets, tabs or the like. However, such fastening means are not illustrated since they are not located in the plane of the section illustrated in FIG. 1.

The lower body member 11 in cooperation with the disc retaining cap 14 defines a disc chamber 16 in which a bimetallic snap disc 17 is positioned. Radial location of the disc 17 is provided by the cap member 14 and axial positioning of the disc is provided by opposed surfaces 18 and 19 of the lower body member 11 and cap member 14, respectively.

The lower body member 11 and the intermediate body member 12 cooperate to define a first switch chamber 21 separated from the disc chamber 16 by a wall section 22. Similarly, the intermediate body 12 and the cap member 13 cooperate to define a second switch chamber 23 separated from the first switch chamber 21 by a wall 24. A first switch 25 is located in the first switch chamber 21 and includes a stationary contact assembly 26 secured on the lower body member 11 by a rivet 27 and a mobile contact assembly 28 secured to the lower body member 11 by a rivet 29. Each of the contact assemblies .26 and 28 provides a terminal portion 31 exterior of the body assembly. The mobile contact assembly includes a cantilever spring arm 32 which extends across the first switch chamber 21 to a free end overlying the inner end of the fixed contact assembly 26.

A second switch 30 is provided in the second switch chamber 23. This switch includes a fixed contact assembly 33 secured to the intermediate body member 12 by a rivet 34 and a mobile contact assembly 36 also secured to the intermediate body member 12 by a rivet 37. Here again, the two contact assemblies 33 and 36 are provided with terminal portions 38 and the mobile contact assembly 36 provides a cantilever spring arm 39 extending across the second switch chamber 23 to a free end overlying the fixed contact assembly 33. In the illustrated embodiment the corresponding contacts of the two switches 25 and 30 have the same shape and are interchangeable.

Operation of the two switches by the disc 17 is provided by a pair of elongated bumper elements 41 and 42. The bumper element 41 extends through and is guided within an opening 43 in the wall portion 22. One end of the bumper 41 is engagable with the central portion of the disc 17 and the other end is engagable with the center portion of the cantilever spring arm 32. The second bumper extends through and is guided within an opening 44 in the wall section 24 of the intermediate body 12. The bumper 42 is engagable at one end with the side of the cantilever spring arm 32 opposite the first bumper 41 and\is engagable at its other end with the central portion of the mobile contact arm 39. The various elements are preferably arranged so that the two bumpers 41 and 42 are in axial alignment and are movable relative to the body assembly along the axis of the disc.

The second bumper 42 is sized so that a small amount of clearance 46 is provided between its ends and one of the cantilever spring arms 32 or 39 when the two switches are in a closed position illustrated in FIG. 1. Similarly, the first bumper 41 is sized to provide a small amount of clearance 47 at one or the other of its ends when the lower switch is closed and the disc 17 is in its downwardly concaved position as illustrated in FIG. 1. In practice, the clearance 46 is obtained by adjustment of a screw 48 which is threaded into the wall portion 22 for engagement of the lower side of the fixed contact. The inner end of the fixed contact assembly 26 is proportioned so that it is engaged by the adjustment screw 48 and bent slightly from its unstressed condition when the proper clearance 46 is provided with respect to the second bumper 42.

Plug members 51 are preferably mounted in the intermediate body member 12 to prevent shorting between the upper rivets 34 and 37 and the associated lower rivets 27 and 29. Similarly, plug members 52 are mounted in the lower body member 11 to prevent shorting between the rivets 27 and 29 and the adjacent portions of the cap member 14.

When the disc 17 snaps from the position illustrated in FIG. I in which it is curved in a direction away from the switches to its opposite position as schematically illustrated in FIG. 4, the bumper 41 is pushed against the mobile contact arm 32 and causes the first switch 25 to open. Opening of the first switch in turn causes movement of the second bumper 42 and results in opening of the second switch 30.

It is recognized that a bimetallic snap disc moves first with creep motion to a position of instability and then snaps through to a second position of stability. Similarly on return movement, the disc moves with creep movement to a position of instability and then snaps back to a first position of stability. Consequently, such a disc has a snap range through which it moves with snap motion in both directions which is less than the distance between the two positions of stability. As used herein the term snap range is intended to mean the range or distance through which the disc snaps in both directions and the disc 17 is illustrated in one extreme of its snap range in FIG. 1 and its other extreme of the snap range in FIG. 4. The snap range is schematically represented by the distance R between the phantom and full line positions of FIG. 4. For purposes of illustration, the movement of the disc is exaggerated in FIGS. 2 through 4.

The clearances 46 and 47 are preferably substantially equal in size and are preferably equal to about one-third of the snap range R. When this relationship exists the disc is in snap motion and has traveled through about one-third of its snap range R before the clearance 47 is taken up and the elements arrive at the first intermediate position illustrated in FIG. 2. Continued movement of the disc to the second intermediate condition of FIG. 3 results in opening of the first switch and taking up of the clearance 46. The position of FIG. 3 is reached while the disc is still in snap motion so continued movement to the final position of FIG. 4 causes the second switch to also open with snap action.

Because the clearance 46 provides a lost motion connection, the first and second switches are opened in sequence rather than simultaneously. Consequently, all of the energy of motion of the disc and the first bumper 41 is available for breaking any welds which might occur between the contacts of the first switch and such welds are completely broken before the second switch starts to open. At the moment the second switch is opened again all the energy of motion of the disc, the two bumpers, and the first switch is available to break any welds which might occur between the contacts of the second switch. Since the welds which may exist are sequentially broken, there is less tendency for the disc to be stalled by welds or the like and consequently, the tendency for the device to fail is reduced.

The clearance 46 between the two switch arms and the bumper 42 also insures that unequal wear of the contacts will not result in a condition in which the first switch blocks the second switch open. For example, if contact wear of the second switch is more rapid than the contact wear of the first switch, the first switch will not block the second switch open unless the difference in wear exceeds the clearance 46. On the other hand if the elements were arranged to open the two switches simultaneously, any wear in the second switch at a faster rate than the wear of the first switch would result in the condition in which the first switch prevented the second switch from closing fully.

Closing of the switches occurs in the opposite sequence as opening in that the second switch or upper switch closes when the disc reaches the intermediate position of FIG. 3 and the first switch does not close until the disc reaches the intermediate position of FIG. 2. However, since both switches remain open until after the disc is in snap motion back toward its first position, both switches close with snap action.

The two switches are separated, in the illustrated embodiment, by the intennediate wall 24 and the bumper 42. Consequently, a buildup of arc splatter in either of the switch cavities does not produce a conductive path between the switches and the danger of arcing between the two switches is substantially eliminated. Preferably, the two switches are located in completely isolated switch cavities in this manner so that higher potential voltage differences can be placed across the two switches without danger of shorting therebetween. It is recognized that the screw 48 provides a conductive path through the wall 22, but this does not provide any difficulty since arc splatter cannot reach the disc chamber and the conductive elements in the disc chamber are sufficiently spaced from the screw to prevent shorting. Therefore, shorting to the disc 17 or the retainer 14 does not occur even when such retainer is grounded and is at a potential difference than the potential of the switches.

With the present invention it is possible to provide a reliable, low cost double pole thermostat which is capable of extended use and is capable of use for controlling relatively large currents and voltages without failure.

Although preferred embodiments of this invention are illustrated, it is to be understood that various modifications and rearrangements of parts may be resorted to without departing from the scope of the invention claimed.

What is claimed is:

I. A thermostat comprising a body assembly, a bimetallic snap disc mounted in said body assembly providing a center portion movable with snap action along a line of action between first and second positions, a first switch mounted on said body assembly providing a first fixed contact and a first mobile contact arm overlying said line of action, said body assembly providing a first support wall extending between said disc and first mobile contact arm providing a first guide opening therein extending along said line of action, a first elongated bumper extending through and guided in said opening engagable at its ends with said center portion of said disc and said mobile contact, said first bumper operating to move said first mobile contact ann into and out of engagement with said first fixed contact in response to said movement of said center portion after said disc is in snap movement, a second switch mounted on said body assembly providing a second fixed contact and a second mobile contact overlying said line of action, said body assembly providing a second support wall extending between said switches and providing a second guide opening therein extending along said line of action, a second elongated bumper coaxial with said first bumper extending through and guided by said second opening engagable at its ends with said mobile contact arms, said second bumper operating to move said second mobile contact into and out of engagement with said second fixed contact in response to movement of said first mobile contact arm after said disc is in snap movement.

2. A thermostat as set forth in claim I wherein said body assembly provides first and second separate switch cavities and a LII vided with lost motion proportioned so that the lost motion of each bumper is substantially equal to one-third of said snap range.

4. A thermostat as set forth in claim 3 wherein adjustment means are provided in said first support wall to adjustably determine the position of said first fixed contact and thereby determine the amount of lost motion of said first bumper. 

1. A thermostat comprising a body assembly, a bimetallic snap disc mounted in said body assembly providing a center portion movable with snap action along a line of action between first and second positions, a first switch mounted on said body assembly providing a first fixed contact and a first mobile contact arm overlying said line of action, said body assembly providing a first support wall extending between said disc and first mobile contact arm providing a first guide opening therein extending along said line of action, a first elongated bumper extending through and guided in said opening engagable at its ends with said center portion of said disc and said mobile contact, said first bumper operating to move said first mobile contact arm into and out of engagement with said first fixed contact in response to said movement of said center portion after said disc is in snap movement, a second switch mounted on said body assembly providing a second fixed contact and a second mobile contact overlying said line of action, said body assembly providing a second support wall extending between said switches and providing a second guide opening therein extending along said line of action, a second elongated bumper coaxial with said first bumper extending through and guided by said second opening engagable at its ends with said mobile contact arms, said second bumper operating to move said second mobile contact into and out of engagement with said second fixed contact in response to movement of said first mobile contact arm after said disc is in snap movement.
 2. A thermostat as set forth in claim 1 wherein said body assembly provides first and second separate switch cavities and a separate disc cavity, one of said switches being located in each switch cavity and said disc means being located in said disc cavity, said switch cavities being substantially totally separated by non-conductive material whereby an accumulation of arc splatter in said switch cavities does not produce a conductive path between said switches.
 3. A thermostat as set forth in claim 1 wherein said center portion of said disc moves with snap action between said positions through a snap range, and each of said bumpers is provided with lost motion proportioned so that the lost motion of each bumper is substantially equal to one-third of said snap range.
 4. A thermostat as set forth in claim 3 wherein adjustment means are provided in said first support wall to adjustably determine the position of said first fixed contact and thereby determine the amount of lost motion of said first bumper. 